It is known that a variety of oil hydraulic equipment such as an oil hydraulic automatic transmission is mounted on an automobile. In such an automobile, a drive loss of oil hydraulic equipment is desirably reduced in order to improve fuel efficiency.
In the oil hydraulic automatic transmission, a seal ring is used. The seal ring is fitted into a shaft inserted into a housing, and seals between the housing and the shaft. Upon driving the automatic transmission, when the shaft rotates to the housing (or when the housing rotates to the shaft), a friction loss is generated between the seal ring and the housing or between the seal ring and the shaft.
Such a friction loss leads to a drive loss of the oil hydraulic equipment. Accordingly, a demanding technology is to decrease the friction loss.
Patent Documents 1 to 5 disclose a technology to decrease the friction loss generated between the seal ring and the shaft. The seal ring disclosed in each Patent Document has a groove on a surface being in contact with the shaft.
If the oil hydraulic pressure is applied to the seal ring, oil enters into the groove. The oil entered into the groove applies a force to the seal ring in a direction away from the shaft. This inhibits a force applied between the seal ring and the shaft, thereby decreasing the friction loss generated between the seal ring and the shaft.